This invention relates to an electrode membrane particularly adapted for use with a gas analysis electrode. Membranes of the type described herein are useful for providing a hydrophobic barrier over an end of a gas electrode, which barrier allows certain gases to penetrate into the electrode and yet blocks the passage of certain liquids therethrough.
In the past such membranes have been formed in sheets of a selected thickness sufficient to allow gas diffusion, with such sheets sandwiched between paper strips or secured to cardboard support members having through openings therein such that a window of the membrane material remained visible.
In practice, the membranes are generally disposed over an opening in the electrode and held in place with an appropriate retaining member such as an O ring, and after such mounting, the paper support is torn or cut away. The electrode is then utilized in an instrument such as a Corning Model 165 or 175 blood gas analyzer. The membrane material is a consumable item and must be changed at various required intervals.
The present invention provides a simplified membrane structure which may be compression-molded into an integral structure thus providing reduced cost and complexity of manufacture. In certain known devices a protective layer of paper is disposed over one side of the membrane and the entire structure may include an array of perforations for assisting in the removal of the paper support ring after use. Other devices contain no such protective layers or perforations and while they are consequently somewhat easier to manufacture, they have a tendency to be more difficult to use.
It has been found that there is a certain difficulty in molding an item of the type described herein since the membrane portion must be of a sufficient thinness to allow gas diffusibility and yet must be molded into a support portion capable of maintaining the membrane portion sufficiently stable of dimension. Thus when the membrane is stretched across the electrode opening, the support portion maintains its dimensional stability and strength and yet allows the membrane to be deformed across said electrode. As mentioned previously, such known support structures have been formed of a paper or cardboard structure with the attendant difficulty of fabrication. In the present invention, a compression mold has been developed which has a profile complimenting that of the article retained therein. The material could thus be molded or formed to a sufficient thinness in an operative region, with a transition zone between the membrane and the support member so that the desired results of practical molding could be achieved. That is, the material forming the membrane structure could flow from the membrane portion to the support member region via the transition zone.